Imaging by means of multifrequency hologram matrix

The fundamental imaging characteristics of the multifrequency hologram matrix are investigated by means of an ultrasound experiment. The range dependence of the point-spread function is analyzed in connection with the experimental configuration of the array and the target area. A design is proposed for the frequency combination and weight function for complex-image superposition which can yield good range resolution. A theoretical derivation is presented for the range resolution of about two wavelengths using five frequencies. Experiments are carried out for three- and five-frequency hologram matrices. The reconstructed image of a point target is investigated in detail and compared with the theoretical value of the point spread function. Reconstructions are made of a target consisting of many points; the results are satisfactory, yielding an improvement in range resolution almost equal to the theoretical value.